Telephone system



June 9, 1936. T. F. CROCKER TELEPHONE SYSTEM Filed Nov. 30, 1934 6 Sheets-Sheet 1 xwa m mm N mvE INVENTOR ZTHOMAS F; CROCKER 'ATTY.

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Patented June 9, 1936 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application November 30, 1934, Serial No. 755,263

21 Claims.

General description The system disclosed herein may be considered as an improvement on the automatic toll switchboard disclosed in the Crocker and Tharp Patent No. 1,883,539, granted October 18, 1932. In the Crocker and Tharp patent, the several sections of the toll switchboard were each specialized for the handling of a given type of traffic, such as (1) traflic incoming over toll lines; (2) traflic origihating at the local automatic exchange and destined to be trunked over toll lines leading to other exchanges; and (3) the handlingof delayed calls, wherein the operator sets up a connection from her position to each of the lines involved, known asa tail-to-tail connection.

A feature of the switchboard disclosed herein isthat an operator at any position of the switchboard may complete any one of the three classes of connections above mentioned. Each position, therefore, is a combination position. In order to enable this tobe accomplished in a practical manner, and in order to simplify and reduce the overall cost of the switching equipment. each toll operators position is provided with a group of finder-selector links, each equipped with a finder which may be referred to as an answering switch, and a selector which may be referred to as a calling switch. To complete any call through her position, the operator causes or permits the answering switch to make connection with the calling circuit and she causes the calling switch to make connection with a desired called circuit.

Since an operator must beable to complete a connection between a toll line in one group and a toll line in another group, all of the toll lines are accessible both to the answering switch and to the calling switch of each finder-selector link. The one-way trunk lines incoming to the switchboard from the local automatic switches of the exchange, however, are accessible to only the answering switches, as they are used for originating calls only. Similarly, the toll-service trunk lines, over which calls are completed by way of automatic switching equipment to the local subscribers of the exchange, are one-way trunk lines and they are accessible to the calling switches only.

In order to enable the operator to direct the operation of the hunting-type answering and calling switches of a link which she may be using, each operators position is provided with a so-called by-pass selector, and this selector has access to all of the toll lines and is provided with circuit arrangements controlled from the operators position equipment so that she can make connection with any toll line through the by-pass selector and cause either the calling switch or the answering switch of a link circuit in use to find and connect with the same toll line. A fea ture of this arrangement is that the operator may cooperate with the distant toll operator to change an established connection from one toll line to another toll line of the same group whenever it appears that the toll line being used is defective. She does this by causing the by-pass selector to make connection with another toll line in the group being used, after which she causes her answering switch or her calling switch, as the case may be, to be reoperated to find the new toll line.

An additional feature of improvement over the arrangement in the above-mentioned patent is that the operator may selectively release the two ends of a connection. This is of. utility particularly in a connection involving a toll line and a local subscribers line. The connection to the local subscribers line may be released immediately, while the connection to the toll line is maintained until the operator has given ring-off supervision over the toll line to the distant operator and has secured the proper response.

A feature of the disclosure is that the operator may cause the calling switch to hunt for and connect with any idle toll-service trunk line (to be used in setting up a connection to a local automatic line) the by-pass selector not being used for this operation.

A further feature of the arrangement is that each position is provided with a group of identity lamps, controlled according to the attained position of the answering switch, to enable the operator to identify the calling group of lines to which the link is connected through the medium of the answering switch. Moreover, the arrangement permits an individual identity lamp to be provided for each line in any desired group so that the operator may know also with which line the answering switch is in connection, as well as the group to which the line belongs. This latter arrangement is of especial utility in enabling an operator to make a repair record when a toll line is found to be defective when a connection has been set up thereove-r.

Another feature of the present disclosure is 7 Description of drawings Referring now to the accompanying drawings, comprising Figs. 1 to 7, they show a sufiicient amount of the apparatus involved in a system embodying the features of the invention to enable the invention to be understood. In order for the drawings to be understood best, the sheets on which Figs. 1, 3, and 4 are drawn should be arranged in order, and the sheets on which Figs. 5 and 6 are drawn should be placed in order, with Fig. 5, part 1, directly below Fig. 3.

Fig. 1 shows the toll line circuit TLC, individual to the toll line TL and accessible to the answering switch AS, Fig. 3, by way of conductors I01 to I N).

Fig. 2 shows the long distance circuit LD incoming from banks of the local selectors and accessible to the answering switch AS, Fig. 3, by way of conductors 201-2HL The circuit LD is sometimes referred to as a C. L. R. (combined line and recording) circuit.

Fig. 3 shows the link circuit LI, provided with an answering switch AS and a calling circuit CS. This link circuit may be compared to a cord circuit in a manual switchboard with the wipers 3| |3l5 corresponding to the calling plug and .the wipers 32|325 corresponding to the answering plug of the cord.

Fig. 4 shows the toll service circuit TSC, which extends from the bank of the calling switch CS to a toll service selector (not shown) through which connections may be set up to the lines of Fig. 7 shows a local circuit LC for use in place of the circuit TSC, Fig. 4, in the event that the switchboard disclosed herein is used in an exchange not having a toll-service trunking systerm, but making use of the regular local automatic switches for the setting up of connections from the toll switchboard to desired automatic lines.

Position arrangement It is assumed, for convenience ofdescription, that the switchboard disclosed is a two-position switchboard, of which the position equipment disclosed in Figs. 5 and 6 is located at the first position. The similar equipment at the second position is not shown, with the exception of the transfer key KN Fig. 5, interconnected with the transfer key Kl! of position i for the purpose of enabling either operator to use her own headset equipment when she is handling calls from both positions, in times or light trafiic.

The cables Cl, C2 and C3, at the first position contain the indicated conductors for making the necessary multiple connections between the common position equipment and the various link circuit, such as the link circuit Ll, Fig. 3. It will be understood, of course, that a sufficient number of these link circuits is provided to handle the estimated trafiic requirements.

The second position also is provided with a group of link circuits, each similar to the link circuit Ll, Fig. 3, and with equipment such as the equipment disclosed in Figs. 5 and 6, common to the group of link circuits.

Link switches The answering switch AS is a rotary switch of a familiar type, and each of its wipers 3 to M5 may have, for example, fifty contacts in the Trunk connections Considering now the connection of trunk lines to the banks of the answering and calling switches, it is to be noted that the first set of indicated contacts in the bankof the answering switch AS is connected through conductors 2il'l2l El with the long-distance or toll-recording circuit LD. It is assumed that the second indicated contact set in the answering-switch bank is also connected to a similar long distance trunk.

The third and fourth indicated contact sets in the answering-switch bank are allotted to the group of toll lines of which toll line TL is one. The second toll line of the group is not shown. It is assumed that the toll line TL extends to a distant automatic exchange, equipped with a. similar automatic toll board.

The fifth and sixth indicated contact sets in the bank of the answering switch are allotted to another group of toll lines (not shown) assumed to extend to a distant manual exchange and having, therefore, a manual toll switchboard.

Considering now the bank of the calling switch CS, the showing of this bank also has been abbreviated so that only six of an assumed fifty contact sets are indicated.

Contact sets I and 2 in the banks of the calling switch, instead of being assigned to long-distance, or toll-recording, trunks, are assigned to trunk lines leading to the toll-service switching system, through which calls are completed to desired local lines. The first set of indicated contacts is connected by way of conductors 311-374 to the toll service circuit TSC, Fig. 4. The second indicated contact set is assumed to be similarly connected to another toll-service circuit.

The third set of indicated contacts in the calling switch CS is assigned to the same toll trunk line associated with the third indicated set of contacts in the bank of the answering switch AS, the contacts being connected with the toll line circuit ILC through the medium of conductors others are not. -For example, the contacts in marking conductors, such as I09, must be mam- 36I, 362, and 363, of the group of conductors- 36l--365 and 365' assigned to serve as the called multiple of the toll line TL. The remaining indicated contacts in the bank of. the calling switch OS are assumed to be similarly connected to the called-multiple conductors of the remaining toll lines which appear as calling lines in the bank of the answering switch AS.

Inter-position multipltng It is to be understood that the banks of the several answering switches at the same position are multipled together by the usual bank multiple and that a similar, but separate, multiple exists as regards the banks of the calling switches such as CS. As regards the relationship of the banks of the answering and calling switches of one position with the banks of the similar switches of the other position, certain of the bank-multiple conductors are common to both positions and "the two positions as regards the lighting of the lamps is not desired. In addition, the second to sixth indicated contacts in the bank of the combination supervisory and marking wipers such as 3M are not multipled between positions,. as the tained local to one position.

However, all the contacts in the banks of the wipers such as 3, 3I2, and 3|3, as well as the first and second indicated contacts in bank of "wiper 3 I 4 are multipled between positions, so that the corresponding conductors are accessible in common from both positions. The reason for the severance of the multiple and the duplication of conductors as regards the two positions will become more apparent as the description progresses.

It is to be noted that conductors such as 201 and I01, etc., are each provided with a short arrow-headed connection extending. diagonally upwards. This symbol has been chosen to indicate that the conductor to which it is applied is multipled into both positions.

At the calling switch CS, it is to be noted that the bank multiple extends through both positions except as regards the banks of the marking wipers, such as the marking wiper 323, which is a separate multiple for each position. It is to be noted that the ones of the conductors shown in association with the calling switch CS which are common to both positions are each provided with the above-mentioned short arrow-headed symbol pointing diagonally upward.

Link equipment In addition to the answering and calling switches AS and CS, the link Ll is provided with answeringand calling-cut-through relays 30! and 304, ring-up relay 302, and the link-connect relay 303, which may be operated to connect the link with the associated position equipment of Figs. 5 and 6. with a combined talking and monitoring key Kl. The remaining equipment which is necessary to the successful operation of the link in the setting up and releasing of connections is to be found in Figs. 5 and 6.

Position equipment The equipment disclosed in Fig. 5 includes the operators head-set, containing the usual trans- In addition, the link is provided mitter and receiver and having associated therewith the repeating coils or induction coils 531 and 532. The relays l-5l9 are provided to control the various operations in a manner to be explained; the keys K4-K8 are associated with the answering end of the links, such as the link LI; and the keys Kl! to KIB are associated with the calling end of the link circuits, such as Ll.

The by-pctss selector Detailed description The disclosure having been described generally, a detailed description of the operation of the apparatus disclosed will now be given. For this purpose a description will first be given of the operations involved in setting up a call outgoing from the exchange in which the automatic toll switchboard is located.

An outgoing call For the purpose of describing the operations involved in completing an outgoing call, it will be assumed now that a subscriber, desiring to converse with a subscriber in a distant exchange, has operated an automatic selector to make connection with a toll-recording or long-distance trunk such as the one associated with the equipment LD, Fig. 2. Connection to the long-distance trunk is made by way of conductors 22], 222, and 223 in the well known manner.

seizing circuit LD; grounding start conductor 212 'Upon the connection being made, line relay 202 energizes over conductors 22| and 223 by way of the left-hand windings of repeating coil 206 and contacts of the ringing relay 20!. Upon energizing, relay 202 closes a circuit for release relay 203 at its inner armature, while at its lower armature it connects the lower talking conductor through contacts of the cut-off relay 204 and the associated small-capacity ring-back condenser to the common intermittent generator lead 2| I. This connection enables the subscriber to hear an intermittent ringing tone to inform him that the connection has been extended to the toll switchboard.

When release relay 203 energizes, under the control of line relay 202, it marks conductor 208 in the banks of the answering switches in both positions by connecting it to the ungrounded, negative pole of the exchange battery by way of cut-off relay B3 and the associated resistor 205 in parallel; it places ground potential on the release-trunk conductor 322 at its inner lower armature so as to maintain the long-distance trunk guarded and to maintain the connection established to the trunk; and at its lower armature it places ground potential on start conductor 2E2, which is common to all of the circuits such as LD and all of the circuits such as TLC.

Conductor 212 is, moreover, common to both sets of position equipment, as indicated by the short arrow-headed line extending diagonally upward from conductor 2H2 in Fig. 3. Therefore, the grounding of start conductor 2! 2 causes a response in both positions.

In the first position, the grounding of conductor 2|2 closes a circuit through contacts of cut-off relay 516 for start relay 501. Start relay 501 thereupon operates and closes a circuit for the answering pilot light 523 so as to give the operator visual indication of the call. Start relay 50'! also closes a circuit at its inner upper armature for the upper winding of the marginally adjusted stop relay l0, by way of contacts of tone connecting relay 504. This upper winding is a rather ineffective winding which does not operate the relay, but produces only a slight pull so as to hasten the operation of the relay responsive to operating current in the lower winding. Start relay 551 also prepares a circuit over drive-answer conductor 34! for whichever answering switch is to respond to the call, and at armature 534 it prepares a test circuit over test-answer conductor 352.

Opera-tor responds In the event that neither of the operators is engaged at the time and the position equipment is, therefore, idle at both positions, the answering pilot lamps, such as 523 are lighted at both positions and both operators may respond to the call. The operator at the first position may respond to the call by throwing the key Kl Fig. 3, to talk-position (assuming that the link Ll is idle, as indicated by the unlighted condition of the busy lamp 336). Upon being operated to talking position, the key Kl connects the driving magnet 3l0 of the answering switch AS to the common drive-answer conductor 34| it connects cut-through relay 30| to the common cutthrough-answer and release-answer conductor 342; it opens a point in the locking circuit of ring-up relay 302 and places ground potential on the identity wiper 3 53; it connects the supervisory and marking wiper 3| 4 to the common mark-answer conductor 345; it prepares a looking circuit for the link-connect relay 303 by way of the common locking conductor 344; and it closes an operating circuit for the link-connect relay 203 over the common operating conductor 343, normally grounded through contacts of the talking relay 502 in the position equipment.

Link-connect relay 303 thereupon operates over conductor 343 and locks itself at its inner lower armature through contacts of the key KI and over conductor 344, in series with talking relay 502.

Relay 502 thereupon operates and disconnects ground from conductor 343, so as to open the initial energizing circuit of the link-connect relay 303 to prevent an operation of a second link-connecting relay in case the operator should inadvertently operate another talking key.

Relay 502 also disconnects the associated talking conductors from the primary winding of the monitoring repeating coil 532 and connects them to the windings of the repeating coil 53! so as to put the circuit into talking condition, at the same time opening a point in the circuit of monitoring relay 50L Link connected to position equipment In the link Ll as a further result of its operanects the answering section over tip-answer and ring-answer conductors 350 and. 351 to the position talking circuit, by way of contacts of split relay 508; connects the calling end of the link circuit Ll by Way of tip-call and ring-call conductors 35! and 356 to the position talking circuit through armatures 542 and 543 to the dialanswer relay 5"; it joins the test and marking wipers 322 and 323 together; it connects the locking circuit of cut-through relay 304 to the common release-call conductor 353; it disconnects driving magnet 320 from the lower winding of relay 304 and the answering supervisory lamp 331; it connects the lower winding of relay 304 and answering supervisory lamp 331 to cutthrough-call conductor 355; and it connects the driving magnet 320 to the common drive-call and supervisory-call conductor 354.

Operating the answering switch relay 501 to the common drive-answer conductor 34!. Since conductor 341 is now connected through contacts of the talking key KI and contacts of the unoperated cut-through relay 30! to the self-interrupting driving magnet 3l0, magnet 3l0 operates in a buzzer-like manner to advance the wipers 3| l3l5 step-by-step in search of the calling circuit.

Finding the calling circuit, LD

The advance of the answering switch continues until the stop relay 506 in the position equipment becomes energized to open the above mentioned circuit of driving magnet 3l0. It is to be noted that ground potential is connected to the lower terminal of the test winding of the marginal stop relay 505 (from the grounded conductor 535 by way of contacts of relays 508 and 505) and that the other terminal of the test winding is connected through armature 534 of start relay 501 to the test-answer conductor 352, which test conductor is now connected through contacts of the linkconnect relay 303 to the test wiper 312 of the answering switch.

The terminals encountered by the test wiper 3l2 in its rotation are either connected to open conductors or to grounded conductors, until wiper 3l2 encounters a terminal associated with a calling circuit, which terminal is supplied with battery potential. That being the case, when Wiper 3l2 reaches the contact to which conductor 208 is connected, it encounters the battery potential impressed on conductor 208 through the upper contacts of release relay 203 of circuit LD by way of resistor 205 and the upper winding of cut-oif relay 204. At this time stop relay 506 in the position equipment is immediately operated to remove ground potential from the answering switch driving conductor 3M and to close a circuit for the tone-connecting relay 504. The removal of ground potential from conductor 3M opens the circuit of driving magnet 3|0 so as to bring the wipers 3!! to 3|5 to rest on the terminal of the calling circuit LD. When the marginally addusted stop relay 506 operates, it is able to remain operated without further current-flow in the lower winding, because of the above-mentioned primary current-flow in its upper winding.

When the tone-connect relay 504 is operated, responsive to the operation of stop relay 506, it applies battery potential through the resistor 536 to the cut-through-answer conductor 342, thereby closing a circuit through contacts of the key Kl for the cut-through relay 30!. Relay 30l now operates and closes a locking circuit for itself through resistor 36'! and driving magnet 3H2, at the same time disconnecting magnet 310 from the common driving conductor 34l it lights the busy lamp 366 at its middle lower armature; it connects up the talking wipers 3 E I and 3 l 5; and it places ground potential directly on test wiper 3I2, thereby guarding the circuit L!) from further seizure.

In the long distance circuit LD, cut-off relay 204, which energized in parallel with resistor 205 and in series with the lower winding of stop relay 406, is maintained energized from the ground potential supplied to conductor 200 through the contacts of cut-through relay 30!. Upon operating, relay 204 at its upper armature by-passes the corresponding contacts of release relay 203 and disconnects the resistor 205 to cut down current consumption; it opens the ring-back-tone circuit at its lower armature; it prepares a disconnect-supervisory circuit over conductor 209 at its inner lower armature; and at its middle lower armature it disconnects ground potential from start conductor 2!! and makes an additional holding ground connection to conductor 222, so as to place the further holding of the connection built up to circuit 'LD under the control of the operator and to permit the calling subscriber to enjoy switchhook signalling without the danger of releasing the connection.

Start relay 50?, Fig. 5, as well as the corresponding relay in the second position, now falls back unless another call has come in in the meantime to cause conductor ZIZ to become grounded at another point, in which case the two start relays remain energized for the time being.

Challenge tone When the tone-connector relay 504 responds to the operation of stop relay 506, as above described, in addition to closing the above-mentioned circuit over conductor 342 to bring about the operation of cut-through relay 301, it opens the circuit of the upper winding of stop relay 506 so as to permit relay 5% to restore responsive to the grounding of conductor 352 at the inner upper armature of the cut-through relay 30l and through contacts of the link-connect relay 303. Stop relay 506 does not restore immediately, however, as the lower winding is short circuited by the ground connection to both its terminals. Relay 506 therefore remains operated for a momentary interval and maintains relay 504 in energized condition.

At its two uppermost armatures, relay 504 disconnects the operators headset conductors from the associated talking'conductors and connects them to the upper winding of the tone relay (or buzzer) 503, while at its inner lower armature it closes a self-interrupting circuit for relay 503, causing relay 503 to operate as a buzzer and thereby produce a challenge tone signal in the operators receiver R, which is associated with the secondary winding of the induction coil 53| in the usual anti-side-tone circuit.

Identifying the calling circuit After a slight interval, relay 566 restores responsive to its lower winding being short circuited and its upper winding being opened. When it does so, it opens the circuit of tone-connect relay 504, whereupon relay 504 restores and terminates the momentary tone application to the operators head-set. When relay 504 restores at this time, it applies ground potential to the upper terminal of the upper winding of identity relay 505, causing relay 505 to operate over conductor 342 and through contacts of the key KI in parallel with the winding of cut-through relay 30l, which is being supplied with holding current through driving magnet 3H? and resistor 361.

When identity relay 505 operates, it disconnects ground potential from the lower terminal winding of relay 505 and from the armature of this relay, and it places a battery potential on conductor lamp 346, obtained through contacts of cut-off relay 516 and resistor 538. The battery potential on lamp conductor 346 brings about the lighting of the identity lamp 33l, assigned to the group of lines or circuits represented by the circuit LD, Fig. 2. This lamp is lighted through Wiper 3|3 and contacts of talking key Kl By the lighting of lamp 33I, the call is identified as a call from a local subscriber.

Waiting fo a call with a talking keg operated take place uninterruptedly responsive to the operation of start relay 501.

Challenging the. calling subscriber Having heard the momentary application of tone current to her headset, brought about by the momentary response of tone-connect relay 504, above described,,the operator now proceeds to challenge the calling subscriber to obtain the necessary information to enable-her to complete r the desired connection.

Let it be assumed that the calling subscriber calls for a number which must be reached by way of the exchange to which the toll line TL, Fig. 1, extends. In this event, the operator proceeds in a manner to be pointed out to cause the calling switch CS to position its wipers on the bank contacts associated with an idle trunk line in the group to which the trunk line TL belongs. Since the calling switch CS is a simple hunting switch and is not provided with step-by-step directive control, the operator operates the by-pass selector BPS, Fig. 6, into association with the desired group of toll lines, whereupon the by-pass selector tests the toll'lines successively and locates an idle one. The calling switch CS is then caused to hunt for and find a terminal marked by the position of the by-pass selector, thus completing the desired connection.

The by-pass selector BPS, Fig. 6, is a combination one-digit and two-digit selector, operating normally as a two-digit selector, that is, the selector ordinarily responds to a level-designating digit to raise its wipers 63|-635 opposite a desired level of contacts and then responds to a group-designating digit to rotate its wipers over the contacts of the selected level into association with the first contact set in a desired group. By this'arrangement, when the number of groups of toll lines is large and some of the toll line groups are small, a single level of contacts may be used to accommodate two or more toll line groups. In the event of two toll line groups being accommodated by a single level of bank contacts, an unused contact set is left between adjacent groups, so that the wipers may be driven onto this unused contact set when all trunks in the preceding group are busy, and the busy-tone signal is transmitted to the operator, while connection is not made with the next following group, as it would be if the intervening dead contact set were not provided.

Of the bank contacts shown in association with the wipers 631-635 of the by-pass selector, the first contact set is assumed to be set No. 1 in the first level, while the contacts shown immediately above are the first set of contacts in the second level. It is assumed that the tollline group including the toll line TL, Fig. 1, and reached through the first level of contacts in the bank of the by-pass selector, is a small group containing less than ten toll lines, and that it, therefore, shares the first level of bank contacts in the by-pass selector with another toll-line group. Since the first toll'line of the group including the toll line TL is connected to the first set of contacts in the first level, the digits 1 and l are assigned to this toll line group.

The operation of the lay-pass selector The operation of the by-pass selector to select an idle toll line and to cause the calling switch CS to connect with this toll line will now be explained.

Having received the desired information from the calling subscriber, the operator leaves the key K1 of the link Ll thrown into talking position (this key is a. locking key, as indicated in the drawing by the letter L) and operates the dial-toll key K15 in her position equipment. When the dial-toll key K15 is thrown, it prepares a circuit at its upper contact for the bridge control relay 510 and split relay 509 in series; it bridges the impulse contacts 562 of the calling device CD'across the disconnected branch of the talking conductors associated with the keys K11 to K16; and at its lower contacts it closes a circuit for selector-seizing relay 519 in series with cut-off relay 516. Cut-off relay 516 now operates to extinguish the identity lamp 331 by disconnecting the resistor 538 from the lamp conductor 346, and it disconnects the incoming start conductor 212 from start relay 5 01, permitting relay 501 to restore and extinguish the answering pilot lamp 523 in case the start relay 501 is still operated because of an unanswered call.

When the selector-seizing relay 519 operates, at armature 549 it transfers the drive-call and supervision-call conductor 354 from supervisory relay 511 and extends it through contacts of dial-answer relay 511 and stop relay 518 to the start conductor 553 of the by-pass selector; it lights the dial pilot lamp 524 at armature 546; and at its inner armature it grounds the holding conductor 554 extending to the by-pass selector BPS, thereby energizing the upper winding of the marginal stop relay 518 preparatory to a quick operation of stop relay 518 through its more eflicient lower winding.

In the by-pass selector BPS, vertical series relay 603 now operates over holding conductor 554 through off normal contacts 611 and prepares a circuit for vertical magnet 615 at its inner lower armature; it opens a. point in a special cut-in circuit for the rotary magnet at its lower armature; and at its upper armature it closes an operating circuit from hold conductor 554 for the cut-in relay 604. Cut-in relay 604 now operates and grounds one terminal of the lower winding of line relay 601 at its inner upper armature to prepare for the operation of the line relay; it makes circuit preparations having to do with the subsequent operation of rotary magnet 616 at its lower armatures; and at its upper armature it opens points in the test circuits of relays 606 and 601, at the same time closing a locking circuit for itself to conductor 554 through the upper contacts of relay 605.

As a further result of the operation of selector-seizing relay 519, armature 548 closes a holding bridge across talking conductors 551 and 558 through the retard coil 520 and the upper contacts of the bridge-control relay 510, and armatures 545 and 541 bring conductors 551 and 558 into connection with the tip and ring conductors 551 and 552 of the by-pass selector. As a result, when cut-in relay 604 operates as described to apply ground potential to the lower windings of line relay 601, line relay 601 is operated through contacts of switching relay 606 and over conductors 551 and 552 through the bridged retard coil 520. Upon operating, line relay 601 closes a circuit for release relay 602 through contacts of the test and switching relays 601 and 606. Release relay 602 thereupon operates and places a shunt around the inner upper contacts of cut-in relay 604, so as to hold line relay 601 operated after relay 604 has restored. At its upper armature it connects up test wiper 633 to prepare a test circuit for relay 601; and at its lower armature it opens a point in the circuit of release magnet 611 and prepares the circuit of vertical magnet 615.

The operator now manipulates the calling device CD in accordance with the first digit (1) in the number (11) assigned to the desired toll line group. When the calling device CD is moved from its normal position, the ofi-normal contacts 5531 close the prepared circuit through the upper contacts of the dial-toll key K15 for bridgecontrol relay 510 and split relay 509 in series. Relay 509 disconnects conductors 551 and 558 from the talking conductors of the operators head-set and from tip-answer and ring-answer conductors 350 and 351, and transfers them to the branch conductors leading to the key group containing the dial-toll key K15, whereat these conductors are connected together through the impulse contacts 562 of the calling device CD, by way of contacts of the dial-toll key K15.

Bridge-control relay 510, at its upper armature, disconnects the retard coil 520 from in bridge of conductors 551 and 558, leaving the line relay 601 of the by-pass selector energized under the control of impulse contacts 562 of the calling device.

When the calling device CD is permitted to return to its normal position, the impulse contacts 56?. are momentarily separated a number of times depending upon the extent to which the calling device was moved, in this case one time. The line relay 601 of the by-pass selector BPS is accordingly momentarily deenergized once. Upon deenergizing, relay 601 momentarily opens the circuit of the slow-acting release relay 602 and closes a circuit through contacts of the operated relays 662 and 663 for vertical magnet H5 and the lower winding of relay 663 in parallel. At this point it may be mentioned that relays 662, 663, and 665 are each provided with a copper sleeve, as indicated, so that each of these relays is slow to release, while having a minimum tendency tobe slow to operate. 6

By the operation of vertical magnet 6|5, the wipers 63|--635 are raised one step so that they stand opposite the first level' of contacts in the associated bank. Off-normal contacts 612 prepare a circuit for release magnet 6I5 when the shaft of the switch is moved from its normal position, while off-normal contacts 6 open the initial circuit of vertical-series relay 663, leaving the continued operation of the relay dependent upon the momentary impulses which the lower winding of the relay receives in parallel with vertical magnet 6l5 during the vertical operation of the switch.

Following the delivery of the momentary impulse to the vertical magnet M5, the slow-acting vertical-series relay 663 restores and opens a point in the circuit of cut-in relay 664 at its upper armature, leaving relay 664 operated in its locking circuit which includes its own upper armature and the upper contacts of rotary series relay 665. At its lower armature, vertical-series relay 663 transiers the operating circuit from vertical magnet M5 to the rotary magnet 6I6, by way of the inner lower contacts of cut-in relay 664 and rotary series relay 665, preparatory to the subsequent operation of magnet 6 I6.

When the calling device CD, Fig. 3, returns to its normal position, contacts 56! separate to permit relays 5H] and 569 to restore. Relay 5I0 restores immediately to re-establish the holding bridge through retard coil 526, while split relay 569 restores a moment later.

When the operator manipulates the calling device CD in accordance with the second digit (1) of the number (11) assigned to the toll line group, the above operations are repeated, with the result that line relay 66! is again momentarily deenergized. This time, relay 661 momentarily closes a circuit through the lower armature of the operated relay 662, the lower armature of the restored vertical-series relay 663,, and the lower armature of the operated cut-in relay for rotary magnet 6l6, by way of rotary series relay 665. Relay 665 is operated in series with'the rotary magnet to establish a new circuit for itself and for the rotary magnet, independent of the inner lower contacts of cut-in relay 664; it opens a point in the hunting circuit of rotary magnet H6 at its inner lower armature; and at its upper armature it opens the locking circuit of cut-in relay 664, permitting relay 664 to restore and prepare the hunting circuit of magnet 6l6.

By the operation of magnet 6l6 responsive to this impulse, the wipers 63 [-635 are brought into engagement with the first set of contacts in the selected level, which in this case is the contacts terminating the conductors 36 |--365.

At the end of a slight interval following the rotary movement, slow-acting series relay 665 restores to start the hunting operation. Upon doing so, relay 665 opens the directive circuit of the rotary magnet at its lower armature; applies ground potential at its two upper armatures to magnet 616 byway of the self-interrupting contacts of magnet 6 l6, inner lower armatures of relays 664 and 665, contacts of the operated line relay 66!, and the lightly adjusted contacts of switching relay 666 and test relay 661. The contacts labeled X are so located as to be the first to operate when the armature, proper, cf the relay starts to move. The hunting action of the by-pass selector BPS now takes place pursuant to the location of an idle toll line in the selected group. This hunting action proceeds until one or both of the relays 662 and 661 is operated responsive to the encountering of a battery poten tial by wipers 633 and 634.

All lines busy in the selected group In the event that all of the lines in the selected group are in use, the rotary movement continues until the wipers 63i635 have been rotated entirely over the group and have arrived on the set of inter-group contacts. The pair of inter,- group contacts engaged by wipers 634 and 635 arestrapped, or connected together, with the result that an energizing circuit is completed by way of the resistor 669 and lower contacts of line relay 661, wipers 635 and 634 (interconnected by the strap on the bank contact they are now engaging), and contacts of relays 661 and 666. When relay 666 energizes it breaks the self-interrupting circuit of magnet 6|6 at its lower contacts, while at its upper contacts it makes a connection from the associated, common busy-tone conductor 635 to the tip conductor I, and it grounds conductor 532 to form a return circuit for the busy tone current, thus informing the operator of the busy condition. Relay 666 also performs the switching-through operation, which will be explained subsequently.

In the event that the last group in the level is being called, the wipers 63l-635 are rotated entirely off the contact bank when they leave the last line in the group, whereupon overflow contacts 6 l 4 are operated to close a circuit for switching relay 666 and cause the operator to be informed of the busy condition.

Sezszng the idle toll Zine TL For the purpose of describing how the call now in progress is completed, it will be assumed that the toll line TL, Fig. 1, is idle when the wipers 631-635 are brought into engagement with the first set of bank contacts in the first level, responsive to the dialling of the second digit 1. In this event, test wiper 633 encounters a battery potential, placed on conductor 363 through the resistor I65 and relay I 63, in parallel and contacts of relay I62. As a result of this encountering of battery potential by test wiper 633, test relay 661 is energized in a circuit from the grounded holding conductor 564, through contacts of relays 665, 664, and 662. Upon operating, relay 66'! quickly breaks the hunting circuit of magnet 6 I 6 at armature 642; at the same armature it places ground potential directly on test wiper 633 so as to mark the toll line engaged; it closes a locking circuit for its lower winding at its inner lower armature from the grounded holding conductor 544 through contacts of relays 665 and 664; at armatures 643 and 644, it connects up wipers 634 and 635; and at armature 6 it closes an energizing circuit for the two windings of switching relay 666 in series, whereupon relay 666 operates.

Upon operatingg'relay 666 disconnects the incoming tip and ring conductors 55! and 552 from the windings of line relay 66!, and extends them through wipers 63l and 632, and by way of talking conductors 36! and. 362 to the talking conductors of the toll line TL, thereby placing the op- "erator immediately into telephonic connection with the toll line.

Line relay 60! restores because it is disconnected by relay 606, and release relay 602 restores also. Relays 60! and 602 prepare a circuit for release magnet 6!!, but the release-magnet circuit is maintained open at armature 642 of relay 60! and at the lower contacts of relay 606.

'In the toll-line circuit TLC, responsive to the ground potential being placed on sleeve conductor it applies ground potential to the junction of resistor I04 and signal relay !02, which operation is of utility in restoring the signal relay when an incoming call over the toll line TL is answered.

Having'thus obtained connection with an idle tollline in the desired group, the operator may now proceed to operate her ringing key so as to signal the operator at the distant toll board in a manner to be explained fully subsequently.

The calling switch C'S operates While the operator is proceeding to signal the distant operator the calling switch CS of the link L! is caused to operate as a finder until it finds the toll line TL, to which connection has been made by the by-pass switch BPS, Fig. 6.

Upon the above-described operation of test relay 60'! of the by-pass selector, start conductor 533 is grounded at the inner upper contacts of relay 60' thereby extending a ground potential by way of the upper armature and testing contact of stop relay 5! 8, armature 544 and its resting contact, and armature 549 of the selector seizing relay 5I9, to drive-call conductor 354. The ground potential on conductor 354 is extended by way of contacts of the operated link-connect relay 303, and the middle lower armature and resting contact of cut-through relay 304 to the driving magnet 320 of the calling switch CS. Selfinterrupting magnet 320 now operates in a buzzer-like manner to drive the wipers 32 !--325 until the circuit of the magnet is opened when stop relay 5 l8 energizes responsive to the arrival of the wipers upon the contacts assigned to the toll line TL with which the by-pass selector BPS is now connected.

Switch CS finds w ll line TL When the wipers 32!-425 arrive on the contacts to which conductors 36!, 363, 364, and 362 (associated with the toll line TL) are connected, test wiper 322 encounters the ground potential placed on the sleeve conductor 363 of toll line TL by way of wiper 633 and armature 642 of the by-pass selector BPS. This ground potential is thereby extended through wipers 322, middle upper armature and resting contact of cut-through relay 304, contacts of the operated link-connect relay 303, and marking test wiper 323 to the marking conductor 364. Marking wiper 634 of the bypass selector is now in engagement with the bank contact of which conductor 364 is connected,

Cat-through relay 303 operates 15 When stop relay 5!8 disconnects start conductor 553 from drive-call conductor 354, it extends it through contacts of relay 5!! and the lower Winding of signal relay 5 I4 to cut-throughcall conductor 355, now connected through con- 0 tacts of link-connect relay 303 to the lower winding of the cut-through relay 304 associated with the calling switch CS. Relays 5!4 and 304 energize in series over this circuit, but the energization of relay 5! does not appear to have any particular utility at this time.

When cut-through relay 304 operates, it closes a locking circuit for itself at its inner upper armature through the resistor 364; disconnects the drive-call and supervisory-call lead 354 from magnet 320 and connects it to the supervisory wiper 324; closes an additional circuit for the busy lamp 336; disconnects test wiper 322 from the marking wiper 323 and connects it to ground, so as to maintain the toll line guarded after the by-pass selector has released; and at its upper and lower armatures it connects up the wipers 32! and 325.

The telephonic connection has now been built up from the calling long distance circuit LD, through the link Ll, to the toll line TL, and it now includes the talking conductors in the position equipment, Fig. 5, because of the operated condition of the link-connect relay 303.

Signaling the distant operator As soon as the operator has dialed the number of the toll line, she manipulates the ringing key 'K! to ring out on the calling end of the circuit. The lower spring combination of the key KI! applies ringing current to the associated ring conductor; the inner upper contacts of the key apply ground potential to the associated tip conductor; and the upper contacts of the key apply ground potential (obtained through con- 5 tacts of the dial-answer key Kl3) to the conductor associated with bridge control and.split relays EM and 509. Relay 5!!) operates to open the control bridge across conductors and 558 including the retard coil 520, while the split relay 509 operates to transfer conductors 55'! and 558 to the branch conductors associated with the keys KI! to KIB. The ringing current is therefore transmitted to the tip and ring conductors of the toll line TL by way of the connection set upthrough the by-pass selector BPS.

As soon as the calling switch CS has been positioned on the toll line TL as above described, a new path for the ringing current is closed through armatures 542 and 543, over tip and ring conductors, 35! and 356 of the cable C3, and thence to the toll line through contacts of the operated link-connect relay 303 and wipers 32! and 325.

When the operator restores her ringing key K, the application of ringingcurrent is terminated and relays 509 and 510 are permitted to restore.

When the distant toll operator responds, she may converse with the originating toll operator and be informed of the destination of the call, whereupon she proceeds to complete the desired connection.

Restoring the lay-pass selector Having conversed with the distant operator, the originating operator now releases the by-pass selector BPS. She does this by restoring the dial-toll key KI5. At the lower contacts of the key, the circuit of relays 599 and tilt are opened, whereupon these relays both restore, and relay 5H5 again permits start relay 5117 to be controlled over start conductor 2| 2.

When selector-seizing relay 5l9 restores, it disconnects the tip and ring conductors 551 and 558 from the corresponding conductors 55l and 552 of the by-pass selector, as well as opening the holding bridge across conductors 551 and 558 through the retard coil 520. Relay 519 also disconnects holding ground from conductor 554, whereupon switching and test relays 666 and 6B! restore. Relay 6M removes ground potential from start conductor 553, whereupon relay 5M restores but cut-through relay 394 remains operated over its locking circuit including resistor 366 Switching and test relays 6% and 601 disconnect the wipers of the by-pass selector and they close a circuit through armature 642 and its resting contact, contacts of relay 5%, and the lower contacts of line and release relays 6!!! and 682, for release magnet 61?, by way of off normal contact EH2. Release magnet 6H operates and causes the by-pass selector BPS to be restored to its normal position, whereupon the releasemagnet circuit is open at off-normal contacts 5 I 2.

Stop relay 5E3 restores when the circuit of its upper winding is opened by the removal of ground potential from hold conductor 554 at the inner contacts of relay 5l9.

The operator permits her key Kl to remain in talking position to maintain the link-connecting relay 3&3 operated until the connection has been extended to the desired line and a response has been secured, or until it has been determined that a response cannot be secured immediately, if such is the case. In the latter case, the operator ordinarily requests the calling subscriber to replace his receiver and wait until he is called back, and the connection islater completed as a delayed call.

The called subscriber answers When the distant subscriber responds, the originating toll operator makes note of the time of the response so that she may determine the length of the conversation.

Operating the split keys In case the operator desires to converse with the calling subscriber while the talking circuit toward the called subscriber is maintained open, she operates the split-call key KIZ, operating the split relay 5529 to disconnect the two sections of the link circuit Ll from each other, leaving the answering section of the link circuit connected to the operators headset. On the other hand, if the operator desires to converse with the operator at the distant toll board or with the called subscriber without the conversation being heard by the calling subscriber, she operates her splitanswer key KB, operating split relay 508 to disconnect the answering end of the link circuit Ll from the operators headset, leaving the operators headset connected to the calling end of the link circuit Ll. Relay 588.01 course restores and again completes the talking circuit between the two ends of the links Ll when the split key K6 is restored.

Freeing 'the position equipment After makingsure that the two subscribers are telephonica'lly connected, the operator restores the key Kl. When this keyis restored, the link connect relay 303 in the link circuit LI and talking relay 502 in the position equipment both restore, but the cut-through relays .301 and 3114 remain energized to maintain the talking circuit complete through the link circuit LI. When the link-connect relay 33.3 restores, the talking circuit is confined to the link circuit Ll, passing through contacts of the link-connect relay, and the temporary association between the operators position equipment of Fig; 5 and the link circuit LI is terminated.

It is to be noted that the talking relay 502 in the position equipment reapplies ground potential topick-up conductor 343, .so .as to enable the operator now to energize the link-connect relay (such as3ll3) in any link circuit when the talking key in such link circuit is thrown,

Monitoring the connection In the event that the operator desires to monitor the connection to ascertain whether or not the two subscribers are conversing properly, she throws the key Kl of the link Ll into monitoring position, thereby connecting conductors 341 and 348 to the .talkingconductors in the link and placing a ground potential on conductor 349. The placing of ground potential on conductor 349 closes a circuit through contacts of the talking relay 502 for the monitoring relay 50],. Relay 5!!! disconnects the receiver R of the ,operatorfs headset from its normal position in the circuit and associates it with the secondary winding of the stepdown monitoring transformer 532, whereby an efficient monitoring circuit is formed which enables the operator to listen in on the circuit while taking a'minimum amount of voice current energy therefrom. The monitoring relay 50I ,restores when the key K1 is restored.

It is to be noted that the conductors leading to the chief operators equipment COE, Fig. 5, part 1, are normally connected across the regular talking leads of the operator's headset, but are switched into parallel relationship with the receiver B when the monitoring relay 5M is operated. .By this arrangement, the chief operator is enabled to listen in with the operator at position 1 at any time to exercise her supervisory func :tions.

Changing tool lines Provisions have been made for enabling the operator to substitute a toll line for one involved in an inter-exchange connection when it appears that the connection set up through a toll line is faulty. This substitution may be made when the the quality of the transmission between the two subscribers by the use of her monitoring key, as above pointed out. Alternatively, the calling subscriber may signal the operator by manipulating his switchhook, causing the calling supervisory lamp 335 to flash in a manner to be pointed out hereinafter. On the other hand, the distant toll operator may be the first to become aware of the faulty transmission and she may signal the originating toll operator by ringing current, causing the ring-up relay 302 to operate and light the calling supervisory lamp 335 and look under the control of the talking portion of the key Kl. For the purpose of the description, however, it will be assumed that the originating operator herself discovers the faulty transmission, whereupon she may operate her talking key Ki and bring about the reoperation of the talking relay 502 and the link-connect relay 303 to bring her into telephonic communication with the two subscribers. She may then explain to the two subscribers that she is about to secure a better connection for them, requesting the two subscribers to wait.

As the next step, the originating operator rnay operate the ring-call key Kl I, bringing about the operation of the split relay 509 to permit ringing current to be transmitted over the tip and ring conductors 35I and 356, through contacts of the operated link-connect relay 303, and through wipers 32l and 325 to the toll line TL. This application of ringing current signals the distant operator, whereupon she comes into telephonic communication with the toll line and converses with the originating operator. 7 Assuming that the exchange to which the toll line TL extends'is an automatic exchange and equipped with the new toll switchboard disclosed herein, each operator proceeds in about the same way to select another toll line. The originating operator manipulates her dial-toll key Ki l, to bring about the hereinbefore described operation of selector seizing relay 5l9 and cut off relay 5I6. The by-pass selector BPS is again seized and prepared for operation. At this time, as before, the operator dials the number 11 assigned to the tollline group, causing the by-pass selector to select the first idle line, the second line in the group, for example. By a similar operation, the distant operator makes connection with the same toll line, as her by-pass selector will also select the first idle toll line in the group.

While still maintaining the dial-toll key Kl5 operated, the operator throws the release-call key KM to break the connection between the calling switchCS of the link LI and the toll line TL. Release-call key KM in addition to operating the bridge control and split relays M0 and 509 places a ground potential on release conductor 353, shunting the locking winding of cut-through relay 304 and causing this relay to restore. When relay 304 restores, the operating magnet is again connected through contacts of the operated link- 304 to become locked again when it reoperates over its lower winding and cut-through-call-conductor 355, when stop relay 5I8 is reoperated to break the hunting circuit of the calling switch and to energize the cut-through-call circuit;

The line of the called subscriber having likewise been connected to the new toll line at the distant end thereof, the conversation between the two subscribers may now be resumed, and the originating operator clears her position equipment by restoring key Kl5, as well as key KI in the link Ll.

Clearing out after conversation conductcr 253 for the calling supervisory lamp 335, by way of wiper 3M and contacts of cutthrough relay 30!. Lamp 335 is now lighted steadily as a disconnect signal.

Freeing the local line immediately Upon perceiving the disconnect signal, the operator may proceed to free the line of the calling subscriber immediately by clearing out the answering, switch AS. To do this, the operator again throws the talking key Kl to bring about the operation of the link-connect relay 303 of the link Li and the talking relay 502 of the position equipment, following which the operator throws the release-answer key K0. The release answer key K8 operates the split-answer relay 508, and it places a ground potential on release-answer conductor 3 32, which closes a shunt, through contacts of the talking key K! in the link circuit, around the winding of cut-through relay 30?, causing this relay to restore and open the 1 connection between the link and the calling line. Resistor 35? limits the current flow through the shunt circuit to prevent a spurious operation of magnet 3").

When cut through relay 30! restores and removes ground potential from test wiper 352 and therefore from conductor 208, cut-off relay 200 of the long distance circuit LD restores and removes ground potential from release trunk conductor 222, permitting the switching apparatus between the calling line and the circuit LD to restore and free the subscribers line for further use.

Clearing out the called end of the connection Having momentarily operated the release-answer key K3 to clear out the calling end of the connection, the operator now throws her ringing key Ki i to signal the distant operator. It will be recalled that the operation of key Ki! results in the operation or" slit relay 509 to connect the branch associated with the key Kl! to condoctors 55? and 558, so that the ringing current passes over the called end of the connection by way of armatures 5 12 and 553 of the dial answer relay 5, conductors 35I and 353, contacts of the link-connect relay 353, contacts of the cut-through relay and the wipers 32l and 325 of the calling switch CS.

When the distant operator responds to the momentary application of ringing current, the two operators converse and the distant operator is told to clear out the connection.

The originating operator now releases the calling end of the connection by momentarily operconnected "to the calling :line.

emaces ating the release-call key KIA. Key KM op- Operations when the desired connectioncannot be completed rz'mmediately In the event that the operator receives a call :as described, over the long-distance circuit LD,

for example, and cannot complete it on the first attempt, (the line maybe busy, or the called subscriber may not be at home) she may request the calling subscriber to wait on the line, or she may inform him "that he :may hang 'up and be recalled when the connection is ready. Assume now that the calling subscriber has replaced his receiver while waiting for the connection to be completed, and that the connection has beencompleted to the desired line and a responsehas been secured. The operator may "request the called subscriber to wait a moment.

She then operates the ring-answer, local, key K4 to recall the calling subscriber. The key K4 operates split relay 508 'to associate tip-answer and ring-answer conductors 350 and 35I with the key; it connects a ringing-current lead to ring-answer conductor 357; and it connects the ungrounded pole of the-exchange battery to the tip-answer conductor 350. Assuming that the .link circuit LI is the one in use, the conductors 656 and 35? are connected through "the switch AS to the long-distance circuit LD,which isstill Therefore ringing relay 201 responds to the potential placed on the associated tip conductor. Upon responding relay 2llI opens the bridge including the right hand repeating-coil windings; it transfers the incoming tip conductor 22I to ground to afford a return path for ringing current, and it transfers incoming ring conductor 223 "to ring conductor $.2I0, thereby permitting ringing current to pass from conductor 2I0-to conductor 22-3, and thence to the called line. I

When .the key K4 is restored, the application of ringing current ceases, and split relay 508 restores, as does ringing relay 20I of circuit LD.

When the calling subscriber responds, line relay 202, which srestored when he hung up and thereby lit lamp 335, reoperates and extinguishes the lamp. r

The conversation may now proceed.

In passing, it may be noted that the ringanswer, toll, key KI-5 is used when the "operator wishes to ring over .a toll .line connected with by the answering switch of a link.

An incoming call In order to explain how a call incomingfrom another exchange (is completed through the toll board to a local line, it will be assumed that the distanttoll operator in the exchange to which the trunk line TL, Fig. .1, extends, has received-a call for a. subscriber .of the exchange served by the illustrated toll board, and that the distantoperator has extended a connection =.to the trunk line 'TLiinithe distant exchange and has applied ringing current momentarily to the trunk line.

In the toll-line circuit TLC, line relay IIII (bridged across the conductors of the toll trunk TL through contacts of cut-off relay I03 and through the associated condenser) responds to the ringing current by vibrating its contacts. A vibrationof the contacts of line relay IOI results 'in the opening of the shunt circuit normally existing around the winding of signal relay I02. Whenthis shunt circuit is opened, signal relay I02 operatesin series with resistor I04 and opens another point in the shunt circuit at its lower armature; it disconnects conductor 363 from the winding of cut-ofi relay I63 and connects it to groundat its upper armature so as to mark the toll line engaged in the banks of the by-pass selectors; it marksthe toll line TL as a calling line by applying "battery potential by way of cut-off relay I63 and resistor I04, in parallel, to conductor I08; and at its lower armature it grounds the start conductor 2I2 to signal an operator through an answering pilot lamp, such as lamp 523, Fig. 5, part 1, or to automatically start an answering switch such as theianswering switch AS in search of the calling line if an operator has a'talking key such as, the key KI thrown on an idle link in readiness for a call to come in automatically to the operator's headset.

Finding the calling circuit TLC It will be assumed that the link circuit LI is the one selected at the first position to take care of the next call and that its answering switch AS, upon operating in the manner hereinbefore described, arrives on the terminals of the toll line TL before an answering switch inthe second posi- .tion does so. Under this condition, stop relay 506 of the position equipment is operated to terminate the hunting movement, in a circuit over test-answer conductor 352, contacts of the linkconnect relay 303, test wiper 3I2, conductor I08, contacts of the operated signal relay I02, and the :resistor I05 andcut-off relay I03, in parallel. As before described, the operation of stop relay 506 results in a momentary operation of tone-connect .relay 504 togive the operator an audible indication, and to place a battery potential on cutthrough-answer conductor 342 by way of the resistor 536 to operate cut-through relay 302 through contacts of the key KI. Cut-through relay 30I thereupon lights the busy lamp 336 and connects up the wipers of the answering switch 'In the toll-line circuit'TLC, cut-off relay I03 is "operated to open the line-relay bridge, to lock itself to conductor I 08 and disconnect resistor I 05, and'to shunt the signal relay I 02 so as to restore it and thereby remove ground potential from the start conductor 2 I2.

Selecting a toll service circuit Upon conversing with the distant operator and finding that the call is to be completed to a subscriber of this exchange, the operator causes the calling switch GS of the link circuit LI to be brought into association with an idle toll-service circuit, suchas the toll service circuit TSC, Fig. 4, through which the connection may be set up. To

do this, the operator throws her dial-automatic Gin ground potential by way of the lower winding of stop relay 5 l 3 to group-hark conductor 358, which is multipled to all of the contacts in the banks of calling-switch marking wipers, such as wiper 323, that are associated with toll-service trunks. This preparesa circuit for stopping the calling switch CS on the contacts of an idle toll-service trunk. Start relay 5i5 also closes a circuit at its inner upper armature through contacts of signal relay 5% for the upper winding of the marginal stop relay 5|3, so as to partially energize relay 5I3 and prepare it to operate very quickly when the circuit prepared through its lower winding and over group-mark conductor 358 is completed. A branch circuit, in multiple with the upper winding of relay 5!3, operates bridge-control relay Eli! and split relay 509 in series. Split relay 509, in addition to transferring conductors 551 and 558'to the branch conductors leading to the key set, now extends ground potential from conductor 535 (grounded at the contacts of the energized talking relay 502) through contacts of the operated start relay 513, and contacts of the unoperated stop and signal relays 5 3 and 5 l 4 and by way of armature 540 to drive-call conductor 354. The placing of the ground potential on conductor 350 at this time closes a circuit through contacts of the operated link-connect relay 303 and through contacts of cut-through relay 304 for the self-interrupting driving magnet 320. Bridge-control relay 5E0 disconnects drive-call conductor 354 from outthrough call conductor 355 (normally interconected through supervisory relay 5! I).

Magnet 320 operates in a buzzer-like manner to drive the wipers 32 !325 until they arrive on the contacts of an idle toll-service trunk, the trunk extending to the toll service circuit TSC, Fig. 4, for example. When this trunk is reached, wiper 322 encounters battery potential on conductor 312, applied through resistor 405 in the tollservice circuit TSC. This battery potential is extended through wiper 323, (connected to wiper 322 through contacts of link-connect relay 303) to group-mark conductor 358. Stop relay 5!3 is therefore operated over conductor 358 to remove ground potential at its upper armature from drive-call conductor 453, thereby permitting the operation of magnet 320 of the calling switch CS, and heaving the wipers 32!-325 in engagement with the bank terminals to which conductors 31! -3'!4 are connected.

Stop relay 5i3 also operates cut-through relay M2 at its inner upper armature, whereupon relay 5! 2 extends ground potential over cut-throughcall conductor 355 and through contacts of relay 303 to cut-through relay 304. Cut-through relay 304 operates and connects up the associated wipers, locking itself energized at its inner upper contacts through the resistor 360.

Stop relay 5I3 also closes a circuit for the upper winding of signal relay 5!4, which includes contacts of the operated relays 5!5, 509, and 502. Upon operating, relay 5!4 locks itself at armature 54! through contacts of relay 5!5; at armature 540 it opens an additional point in the circuit through which ground potential was previously applied to conductor 354; and at its inner upper contacts it opens the circuit of the upper winding of relay 5E3 and the circuit of relays 5!!) and 509. Relays 5H3 and 500 restore, and relay 5!3 restores also, as its circuit over conductor 358 has been opened at contacts of the cut-through relay 304. Cut-through relay 5|2 is restored by relay 5!3.

At its upper armature, signal 5! 4 closes a circuit for the dial-pilot lamp 524 to inform the operator that she may now operate the dial of the calling device CD in accordance with the digits in the desired number.

Seizure of the toll service circuit When the supervisory wiper 324 is connected up at the contacts of cut-through relay 304, a circuit is closed over supervisory conductor 313 for switching relay 40! in the toll service circuit TSC. This circuit includes contacts of the operated link-connect relay 303, supervisory-call conductor 354, armature 549 and its resting contact, contacts of the bridge-control relay 5!0, supervisory relay 5! l, and resistor 531. Relay 5!! does not operate over this circuit in series with the high resistance upper winding of relay 40!. The lamp 331 is therefore not now lighted.

In the toll service circuit TSC, when relay operates over supervisory lead 313, it opens the by-pass connections around the windings of the repeating coil 402, bridging the left-hand repeating-coil windings across the incoming conductors 31'! and 314, and bridging the right-hand repeating-coil windings across the outgoing conductors 406 and 408. The line relay (not shown) of the toll service selector to which conductors 405408 extend, now operates over conductors 406 and 400 in series with the lower winding of electropolarized supervisory relay 403 to prepare the toll-service selector for operation. The polariz ing winding of relay 403 is energized from the grounded release-trunk conductor 312 through contacts of the operated relay 40! and resistor 409. The current now flows through the lower Winding of supervisory relay 403 in such a direc- 3 tion as to oppose the polarizing winding of the relay. Relay 403 therefore does not now operate.

Dialing the desired number When the operator turns the calling device CD from its normal position, the off-normal contacts 56! close a circuit through contacts of the key Kl6 for bridge-control relay 5l0 and split relay 509 in series. Relay 509 operates to connect conductors 551 and 558 to the impulse con- 4 tacts 562 of the calling device CD, and bridgecontrol relay 5!0 disconnects the battery potential (applied by way of resistor 53'! and supervisory relay 5!!) from drive-call and supervisory-call conductor 354, thereby opening the circuit of switching relay 40! in the toll service circuit TSC, Fig. 4.

Relay 40! by-passes the windings of the repeating coil 402 and opens both the front and back bridges of the circuit TSC, so that incoming conductor 31! is extended through contacts of relay 40! to conductor 408, and the incoming conductor 314 is extended through contacts of relay 40! to the outgoing conductor 406.

The line relay (not shown) of the toll service selector to which conductors 406 and 408 extend is now held operated over conductors 31!314, wipers 32! and 325, contacts of the link-connect relay 303, tip-call and ring-call conductors 35! and 356, armatures 542 and 543, conductors 551 and 558, contacts of the operated split relay 509, contacts of dial-automatic key KI6, and the impulse contacts 562 of the calling device CD. This transfer is made, it will be noted without any interruption in the continuity of the circuit extending to the line relay of the toll service selector, as the split relay 509 operates first to prepare the circuit while switching relay of the toll-service circuit transfers the line relay from the holding bridge (through relays 403) throu h tion equipment both restores.

Relay 5l0 again applies a battery potential through resistor 531 and the windingrof the marginal supervisory relay 5 to conductor 4, bringing about the above described operation of switching relay The same operations are repeated each time the calling device CD is operated in accordance with a succeeding digit in the desired number.

I die-Zine supervision After the final digit hasbeen dialed, and the connection has been finally completed to the called line, and in the event that the called line is idle, current-flow is reversed in the well known manner in the conductors 406 and 408 outgoing from toll service circuit TSC, whereupon the electro-polarized supervisory relay 403 Operates and removes the shunt from aroundthe winding of the supervision-repeating relay 404. Relay 404 now operates and shunts the low resistance lower winding of relay 4! around the high resistance upper winding of the relay, thereby so increasing the current-flow over conductor 313 and through the marginal supervisory relay 5 to cause relay 5| 1 to operate andbring about the operation of cut-through relay 512. Relay 512 applies ground potential to cut-through-call conductor 355, thereby lighting supervisory lamp 331 through contacts of relay 303 to indicate that the called line is idle and that connection has been made thereto.

The operator may now converse: with the.

originating operator and discover whether or not the originating operator is ready for the called subscriber to be signalled.

When the called subscribed is to be signalled,

" the operator manipulates the ring-call key Kl I,

thereby applying ringing current to the associated branch of the talking conductors and operating bridge-control and split relays 5I0 and 509 through contacts of the unoperated dial-answer key Kl3. Bridge-control relay 5l0 opens the. supervisory and bridge-control circuit at its inner upper armature, whereupon relay 40I of the toll service circuit TSC and relay 5| I in the posi- Relay 5 restores cut-through relay 5l2 to extinguish the supervisory lamp 331, and relay 40l clears the circuit TSC for the through passage of ringing current.

Responsive to this application of ringing current, the usual automatic ringing is started, whereby the called subscriberis signalled in the usual manner. 7

When the ring-call key Kll is restored, relays 509 and 515 restore, and relays 5| l, M2, and 40! reoperate, and lamp 331 is relighted.

Answering supervision When the called subscriber responds, the usual ring-cut-off operation takes place, and currentflow in the outgoing conductors oi the trunk circuit TSC is discontinued for the period of the conversation. At this point supervision-repeating relay 404 falls back to extinguish lamp 40!. This indication is relayed by supervisory relay 5i i, which restores and thereby causesrelay'5l2 to restore and finally extinguish lamp 331 to give answering supervision.

The operator may now restore her talking key KI, and thereby restore link-connect relay 3,03, whereby'her position equipment is freed. and cleared out for further use in association with other links.

With the link-connect key restored, voice currents may pass directly through the strands of the link Ll without traversing the position equipment. Moreover, the answering-supervisory lamp 3-31is now connected directly to the supervisory wiper 324, through contacts of the operat- 1 ed cut-through relay 304 and contacts of the restored link-connect relay 303. From this point on, lamp 331 is light or not, depending upon whether the supervision-repeating relay 404 is operated or not, as the lamp will not glow in series with the upper winding of relay 40!.

Having caused the connection to be completed in the manner above pointed out, the operator proceeds with her other duties and paysno further attention to the established connection until she receives a disconnect or a recall signal.

Changing toll lines In order to explain how the operator is able to change toll lines when the toll line in use proves to be defective for conversational purposes, it will be assumed that the distant operator, upon listening in during conversation, discovers. that the transmission over the toll line TL is faulty. Under this condition, the distant operator projects ringing current over the toll line TL to operate the bridged ring-up relay 302 in the link circuit Ll. Relay 392 operates. and locks itself through contacts of the key Kl, at the same time closing a lighting circuit for the calling .supervisory re-= lay 335.

When the operator throws the key Kl to talking position, so as to energize the link-connect relay 334-and the talking relay 502 in the position equipment, ring-up relay 302 is restored and the calling supervisory lamp 335 becomes extinguished. The distant toll operator then informs the completing operator of the faulty condition of the toll line TL and requests her to make connection with another toll line in the same group so that the connection may be rerouted over the other toll line. In order to do this, the operator proceeds in somewhat the same manner as hereinbefore described to position the by-pass selector BPS on the first idle toll line in the groupincluding the toll line TL and to cause the answering switch AS to be repositioned on the new toll line. Since she now desires to reposition the answering switch AS, the, operator throws the dialanswer key KI3. The dial answer-key'Kla, in addition to making the connections made by the dial-tone key Kl1- closes a circuit for dial-answer relay 5|1 in series with cut-off relay 5H5. As a result, relays 5H5, 5H1, and 5i9 are now operated, and relay 5I9 brings about the seizure of the by-- pass selector BPS and the preparation of this selector for operation. Relay 5I-1, at its' lower armature, prepares a new energizing circuit by way of the resistor 539 for cut-through-answer conductor 342; disconnects the test winding of the stop relay 5l8 from the mark-call lead 555 and connects itto the mark-answer lead 556, so as to mark a conductor in, the bank of the answering switch AS instead of in the bank of the calling switch CS; at armature 544 it transfers start conductor 553 into association with the driveanswer lead 34]; at its inner upper armature it disconnects the cut-through-call lead 355 so that it will not become grounded upon the operation of stop relay 5I8; it disconnects the tip-call and ring-call conductors at armatures 542 and 543 so as to isolate the called substation for the time being; and at its upper armature it grounds the mark-answer conductor 345 so as to enable the marking circuit to be subsequently completed by way of wiper 3I4 of the answering switch AS.

It is to be noted that ground potential is now removed from the upper contact pair of the ringcall key KH and of the ring-answer key K5, so that neither of the ringing keys K5 and KH is able to operate its associated split relay (598 and 599) and the operator is now unable to ring out over either end of her position equipment.

When the operator manipulates her calling device CD in accordance with the two-digit number assigned to the toll line group including the toll line TL, the by-pass selector BPS operates as hereinbefore described to search over the group. It will be assumed now that the second toll line in the group is idle. The second toll line therefore is seized by the operation of relays 606 and 60! of the by-pass selector, which takes place as hereinbefore described. The conductor corresponding to conductor 363 and associated with the second toll line is grounded, and the cut-oil relay corresponding to relay Hi3 of the circuit TLC Fig. 1, is operated as a result.

The operator now momentarily operates her release-answer key K8. Key K8 operates the split relay 508 so as to disconnect the answering end of the link circuit L! from the operators headset for the time being, and it places a ground potential on release-answer conductor 342, thereby closing a shunt circuit, through contacts of the key Kl, around the winding of cut-through relay 30L Relay 3M thereupon restores and opens its locking circuit atits upper armature. With cut-through relay 30! restored and with grounded start conductor 553 of the by-pass selector BPS (now grounded at contacts of test relay 557) connected to drive-answer conductor 34I at armature 544 of the operated dial-answer relay 5H, the self-interrupting drive magnet am of the answering switch AS now operates through contacts of the talk key Kl to drive the wipers 3| l3l5 until the driving circuit is opened upon the operation of stop relay 5l8. Relay 5l8 operates when the toll line selected by the by-pass selector BPS is reached.

It will be recalled that mark-answer conductor 345 is grounded in the position equipment at the upper contacts of the dial-answer relay 5. The grounded mark-answer conductor 345 is connected through contacts of the key K! to the supervisory and marking wiper 364. Now, when the wipers of the answering switch AS reach the fourth set of bank contacts shown, they are connected with the second toll line in the group including the toll line TL. The nowgrounded wiper 3l4 therefore extends ground potential over the marking conductor of the second toll line (correspcnding to marking conductor I39 of the toll line TL). This conductor extends to and connects with a marking conductor (similar to the marking conductor 365) which extends to the bank of the by-pass selector. The wiper 635 is now standing on the bank contact to which the marking conductor of the second toll line (corresponding to conductor 355 of the toll line TL) is connected. Ground potential, therefore, is extended through wiper 635, armature 644, conductor 556, and the lower armature of the operated dial-answer relay 5 ll, to the operating winding of stop relay 5l8. Relay 5l8 now operates and opens the above-traced driving circuit of magnet 3H3 of the answering switch AS at its upper armature, leaving the wipers of the answering switch in association with the second toll line of the group including the toll line TL.

As a further result of its operation, stop relay 5l8 extends an energizing potential to cut through conductor 342, from the resistor 539, closing a circuit through contacts of the key K! for the cut-through relay 3!. Relay 30| now reoperates and connects up the associated wipers, in addition to again locking itself at its upper armature through the resistor 331 and operating magnet 3H].

It will be understood, of course, that the operator is in telephonic communication with the newly selected toll line as soon as this toll line has been seized by the by-pass selector BPS, and that a second talking connection to the toll line is completed from the operators headset by way of the wipers of the answering switch AS, when this switch is positioned on the new toll line as above described. The operator is informed of the final positioning of the answering switch AS and the operation of the cut-through relay 33l when the calling supervisory lamp 335 becomes lighted through contacts of the cut-through relay 301 because of the ground potential now supplied over conductor 345 to marking wiper 3M as above pointed out.

The operator may now restore the dial-answer key Kl3, whereupon relays SH], 5, and M6 restore and the by-pass selecter BPS releases. When cut-off relay 5E6 restores, battery potential is applied by way of resistor 538 and contacts of the operated identity relay 505 to conductor 34S, causing the identity lamp 333 associated with the second toll line in the group in question to become lighted through wiper3| 3 and contacts of the operated key Kl. The operator is thereby informed of the particular trunk line in the group with which he has made connection. It may be pointed out that the upper winding of identity relay 555 is energized over cut-through-answer conductor in parallel with the winding of relay 3M of the link Ll.

With the above mentioned restoration of dialanswering relay 5, the tip-call and ring-call conductors 35I and 35B are again connected up at armatures 542 and 543 to the position talking circuit so that the two subscribers may start their conversation, even while the talking key Kl is in operated position, or at any rate the called subscriber may be informed by the operator that he may now proceed with the conversation.

A similar substitution having been made by the distant operator in substantially-the same way, the two subscribers may converse as desired over the new toll line. The talking circuit includes only the strands of the link Ll, as soon as the operator restores the key KI and permits the link-connect relay 303 to restore.

It will be understood, of course, that the trunk lines such as TL are connected up in the same order in the banks of the by-pass switches in both exchanges, so that both the by-pass switches will select the same idle toll line under conditions similar to those described above.

Clearing out after conversation When the subscribers replace their receivers 

